Geochemistry and U-Pb age of zircon from Pizhemskoe titanium deposit (Middle Timan)

The geochemical studies are devoted to the memory of Academician N. P. Yushkin, who during his life paid much attention to this scientific direction. For the first time zircons from the titanium ores of Pizhemskoe deposit were analyzed with local dating (U-Pb method, SHRIMPII). The wide range of age values within the interval from 2740 Ma to 334 Ma was determined. The ages could be arranged into three groups: neoproterozoic (5 points), meso- paleoproterozoic (26 points), archaean (3 points) with marked polymodal distribution of maximums in the intervals of 600, 900, 1000-1600, 1600-2000 and 2660-2740 Ma. The geochemical type of zircon with xenotime heterovalent isomorphism (Zr+Si)4+  (Y+REE)3+ + P5+ was determined. The relatively low Y + REE content in the range of 150 to 3000 ppm is common for the majority of grains. However the data selecting includes more than 10 % of zircon grains with anomalously high total content of these elements up to 1-3.5 % wt., which also correlates with P content. The obtained material corresponds to the dating results and geochemistry of zircons selected from overlying conglomerate-breccia bed of the Ichetyu occurrence and chetlasskiy lamprophyres. The specific «Timansky» type of yttrium-phosphorus-rare-earth zircon was determined. This fact proves a single zircon source for both industrial sites. In addition zircon could originate from different depth levels of underlying crystal basement. The zircon dating shows that the titaniferous formation is elder than it was considered earlier (Middle Devonian) and its age should be estimated as Precambrian.